Final answer:
The Thames River has more water in it by the time it reaches London compared to Lechlade due to increased rainfall in London and tributaries adding water along the course of the river.
Step-by-step explanation:
The Thames River experiences a notable increase in water volume as it flows from Lechlade to London, influenced by multiple factors. A primary contributor is the heightened rainfall in London, where the city's average annual precipitation surpasses that of Lechlade. This increased rainfall directly adds more water to the river as it progresses downstream. Additionally, the Thames benefits from the influx of tributaries along its course, such as the River Brent, River Wandle, and River Lea, augmenting its water content.
While Lechlade may experience some evaporation, contributing to a minor decrease in water volume, the cumulative effect of increased rainfall and tributary contributions amplifies the Thames's water capacity as it approaches London. This dynamic interplay of climatic and geographical factors shapes the river's hydrological profile along its course.